Tape Cartridge Having Tape Media With Longitudinally Shifted Servo Pattern for Increased Sampling Rate

ABSTRACT

A magnetic tape cartridge including magnetic tape with servo information is provided. The servo information comprises a plurality of parallel longitudinal servo bands that lie between a plurality of longitudinal data bands. The plurality of servo bands include odd servo bands and even servo bands, wherein each of the odd servo bands lie between each of the even servo bands. Each of the plurality servo bands include a plurality of frames, wherein each frame includes a plurality of bursts of transition stripes, and each burst having a first transition stripe. The first transition stripe of each burst of each the odd servo band is longitudinally shifted from the first transition stripe of each burst of each even servo band by a substantially equal distance, D, such that servo information of the odd servo bands is interleaved with the servo information from the even servo bands.

DOCUMENT INCORPORATED BY REFERENCE

Commonly assigned U.S. Pat. No. 5,689,384 is incorporated for itsshowing of a timing based servo system.

FIELD OF THE INVENTION

This invention relates to a tape cartridge having a servo pattern, andmore particularly, to a magnetic tape of the tape cartridge havingtiming based servo band(s) extending in the longitudinal direction ofthe magnetic tape.

BACKGROUND OF THE INVENTION

Magnetic tape provides a means for physically storing data which may bearchived or which may be stored in storage shelves of automated datastorage libraries and accessed when required. The reading and/or writingof data in bands on magnetic recording tape requires precise positioningof a magnetic head. The magnetic head must be moved to, and maintainedcentered over, specific longitudinal data bands, as the magnetic tape ismoved longitudinally past the magnetic head. The magnetic head istranslated between bands in a lateral direction with respect to thelongitudinal data bands.

A servo system is employed to move the magnetic head to and position themagnetic head in the center of the desired data band or bands, and totrack follow the center of the desired data band or bands. The databands are becoming increasingly smaller and closer together in order toincrease the data band density and thereby increase data capacity of agiven tape. Hence, it has become desirable to place the longitudinaldefined servo bands at various locations across the full width of thetape, separated by groups of data bands. This allows the servo bands tobe close to the data bands and limits offsets due to tape stretch, etc.This also allows a greater number of bands to be employed due to thegreater precision of the relationship between the servo bands and thedata bands.

SUMMARY OF THE INVENTION

A magnetic tape cartridge including magnetic tape with servo informationis provided. The servo information comprises a plurality of parallellongitudinal servo bands that lie between a plurality of longitudinaldata bands. The plurality of servo bands include odd servo bands andeven servo bands, wherein each of the odd servo bands lie between eachof the even servo bands. Each of the plurality servo bands include aplurality of frames, wherein each frame includes a plurality of burstsof transition stripes, and each burst having a first transition stripe.The first transition stripe of each burst of each the odd servo band islongitudinally shifted from the first transition stripe of each burst ofeach even servo band by a substantially equal distance, D, such thatservo information of the odd servo bands is interleaved with the servoinformation from the even servo bands.

The frame includes a first burst of transition stripes in a firstazimuthal orientation and a second burst of transition stripes in asecond azimuthal orientation different than the first azimuthalorientation, followed by a third burst of transition stripes in thefirst azimuthal orientation and a fourth burst of transition stripes inthe second azimuthal orientation and wherein a distance between thefirst transition stripe of the first burst and the first transitionstripe of the third burst is a distance B. In one embodiment the secondazimuthal orientation is opposite of the first azimuthal orientation.

In one embodiment the magnetic tape is configured for a tape drivehaving a plurality of servo read elements, the first transition stripeof each burst of each the odd servo band is longitudinally shifted fromthe first transition stripe of each burst of each the even servo band bya substantially equal distance, D, wherein${0.9\frac{B}{X}} \leq D \leq {1.1\frac{B}{X}}$and wherein X is a number servo read elements of the tape drive.

Accordingly, in one embodiment the magnetic tape is configured for atape drive having two servo read elements such that 0.45B≦D≦0.55. Inanother embodiment the magnetic tape is configured for a tape drivehaving three servo read elements such that 0.30B≦D≦0.37B.

In one embodiment the magnetic tape comprises five parallel longitudinalservo bands. Further the frame may further include a first burst of agroup of five stripes in a first azimuthal orientation and a secondburst of a group of five transitions in a second azimuthal orientationdifferent than the first azimuthal orientation, followed by a thirdburst of a group of four transition stripes in the first azimuthalorientation and a fourth burst a group of four transition stripes in thesecond azimuthal orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a magnetic tape having a timingbased servo track, and of a magnetic head and servo system of a magnetictape drive having multiple servo read elements;

FIG. 2 is a simplified diagrammatic illustration of a magnetic tapehaving a timing based servo track, and of a magnetic head and servosystem of a magnetic tape drive having multiple servo read elementsincluding indication of “A” and “B” signal intervals;

FIG. 3 an embodiment in accordance with the present disclosure of adiagrammatic illustration of a magnetic tape having a timing based servotrack, and of a magnetic head and servo system of a magnetic tape drivehaving multiple servo read elements;

FIG. 4 is an embodiment in accordance with the present disclosure of asimplified diagrammatic illustration of a magnetic tape having a timingbased servo track, and of a magnetic head and servo system of a magnetictape drive having multiple servo read elements including indication of“A” and “B” signal intervals;

FIG. 5 is an illustration of a magnetic tape drive in accordance withthe present disclosure; and

FIG. 6 is a detailed illustration of a magnetic tape cartridge inaccordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The following is intended to provide a detailed description of anexample of the invention and should not be taken to be limiting of theinvention itself. Rather, any number of variations may fall within thescope of the invention which is defined in the claims following thedescription.

Referring to FIG. 1, a timing based servo pattern is described on amagnetic tape, such as magnetic tape 20 wherein prerecorded magneticparallel longitudinal servo bands 27 (e.g. 27 a, 27 b, 27 c, 27 d, and27 e) lie between groups of longitudinal data tracks 29 (e.g. 29 a, 29b, 29 c, 29 d, and 29 e). In addition, the magnetic tape 20 is providedwith guard bands 48, 49 at the edges of the tape. The longitudinaldirection is defined as the direction along the length of the magnetictape 20. The lateral direction is defined as the direction along thewidth of the magnetic tape 20 and is perpendicular to the longitudinaldirection. The terms “band” and “track” are used interchangeably herein.Similarly, the terms “bands” and “tracks” are used interchangeablyherein.

In the specific example of FIG. 1, five longitudinal timing baseddefined servo bands 27 are prerecorded on a magnetic tape 20 for trackfollowing at these positions. The pattern of magnetic transitionsrecorded in the defined servo bands is a repeated set of frames 38, eachof which are of different azimuthal orientations. For example, thepattern may comprise transitions slanted, or having an azimuthalorientation, in a first direction with respect to the longitudinaldirection of the linear servo track, alternating with transitions havingdifferent slants, for example, in the opposite direction. The groups oftransitions having the same azimuthal orientation and separated by gapsor spaces are referred to as “servo bursts” or simply as “bursts” (e.g.bursts 40, 41, 42, and 43). Each servo burst contains a predeterminednumber of transition stripes per burst, which can be used in errordetection and correction.

The head assembly 24 comprises a plurality of read and/or write elements28 configured to read and/or write data on a magnetic tape with respectto sets of the longitudinal data tracks 29. In the example of FIG. 1, ahead assembly 24 comprises at least two narrow servo read elements 25,26, allowing two servo bands to be sensed simultaneously. The resultingoutputs from both servo bands may be averaged or used redundantly toreduce error rates. When the servo read elements 25, 26 are properlypositioned at the defined servo bands 27, the read and write elements 28are properly positioned to transfer data with respect to the data tracklocation of the magnetic tape 20.

Those skilled in the art will recognize that the dark slanted stripesrepresent magnetized areas of recorded magnetic flux that extend acrossthe width of a servo track 27, and that the edges of the stripescomprise flux transitions that are detected to generate a servo readelement signal. The transitions have two magnetic polarities, on eachedge of a stripe. When a servo read element crosses a transition ofservo track 27, e.g. along servo track centerline 50 of FIG. 2, itproduces an analog signal pulse whose polarity is determined by thepolarity of the transition. For example, the servo read element mayproduce positive pulses on the leading edge of each stripe (onencountering the transition of encountering the stripe), and negativepulses on the trailing edge (on encountering the transition on leavingthe stripe). To reduce the chance for error, the servo system times onlyintervals between magnetic flux transitions having the same polarity. Asone example, only transition pulses generated by the servo read elementin moving across the leading edge of a stripe are used, and transitionpulses generated by moving across the trailing edge of a stripe areignored. Hence, herein, the term “transition” refers to edges ofstripes, or equivalent, that result in the generation of signals havingthe same polarity.

The lateral positioning of the servo read element with respect to thetiming based servo track is sensed based on a measure of time betweentwo transitions having different slants, called the “A” distance, ascompared to the time between two transitions having parallel slants,called the “B” distance. Referring to FIG. 1 for example, the “A”distance may be measured based on the time between the first transitionstripe of burst 40 and the first transition stripe of burst 41. Further,in one example, the “B” distance is measured based on the time betweenthe first transition stripe of burst 40 and the first transition stripeof burst 42. One of ordinary skill in the art would understand thatwhile in the above example the first transition stripe of each burst isused to determine the “A” and “B” distance, any transition stripe of therespective burst may be utilized. For example, the “A” and “B” distancesmay be determined based on the comparison of the second transitionstripe of one burst against the second transition stripe of the otherburst. The first transition stripe is defined herein as the firsttransition stripe the servo read element 25, 26 arrives at in the readdirection.

More specifically, lateral position sensing within a defined servo bandis achieved by deriving a ratio of these two servo pattern intervals. Inparticular, the lateral position may be the ratio of (1) the distancebetween transitions of bursts 40 and 41, called the “A” distance, to (2)the distance between transitions of burst 40 and 42, called the “B”distance. The distances are measured by the timing between thetransitions at a constant velocity. Thus, as the tape head servo readelements 25, 26 move toward the lower edge of the tape 20, the ratio ofthe time between the transitions of burst 40 and 41 to the time betweenthe transitions of bursts 40 and 42 becomes greater, since the distancebetween the “A” transitions of the burst 40 and 41 is greater, while thedistance between the “B” transitions of burst 40 and 42 remainsunchanged.

It is important to note that the servo tracks 27 are typically generatedby a servo writer having two spaced apart write elements of differentslants, forming the “A” distance, which are pulsed simultaneously. Thus,the “A” geometric distance is determined photolithographically, and istherefore, independent of the timing or the velocity of the servo writerdrive.

The tape is moved longitudinally across the head assembly 24 so that theservo tracks 27 a and 27 b are moved across the servo read elements 25and 26, respectively. When such movement occurs, the servo pattern ofmagnetic flux transitions is detected by the servo read elements 25 and26 so that it generates two analog servo read element signals, one foreach servo read element 25 and 26. The analog servo read element signalsfor each servo read element 25 and 26 are provided via a servo signallines 84 and 90 to signal decoders 86 and 92, respectively. Therespective signal decoders then process the servo read element signalsand generate a position signal that is transmitted via position signallines 88 and 94 to servo controller 80. The servo controller 80generates a servo control signal and provides it on control line(s) 82to a servo positioning mechanism at head assembly 24. The servopositioning mechanism responds to the control signal from the servocontroller 80 by moving the assembly including servo read elements 25and 26 laterally with respect to the servo track centerline 50 to reachthe desired servo track or to maintain the servo read elements 25 and 26center with respect to the servo track centerline 50.

Servo detection logic of servo system 80 is configured to detect fromthe signals supplied on line(s) 82, the relative timings of thelaterally extending transitions, specifically including the transitionshaving different slants, sensed by the plurality of laterally spacedservo read elements 25 and 26 as the magnetic tape 20 is moved in thelongitudinal direction. The servo detection logic is configured todetermine from the relative timings of the sensed transitions the “A”distances and information regarding the relationship between theplurality of servo read elements 25 and 26 and the magnetic tape for atleast one known set of laterally extending transitions having differingslants.

FIG. 2 shows simplified version of a timing based servo pattern on amagnetic tape, such as magnetic tape 20. For purposes of simplifying theillustration each burst is shown in FIG. 2 as a single line. In oneembodiment the single line may represent the first transition stripe ofeach burst.

Similar to that described with respect to FIG. 1, the head assembly 24comprises at least two narrow servo read elements 25, 26, allowing twoservo bands (e.g. 27 a and 27 b) to be sensed simultaneously. Asmentioned above, when a servo read element (e.g. servo read element 25and/or 26) crosses a transition of servo track 27, e.g. along servotrack centerline 50, it produces an analog signal pulse whose polarityis determined by the polarity of the transition.

In the example illustrated in FIG. 2, transition stripe L2, having afirst azimuthal orientation, is separated from transition stripe L3,having a second azimuthal orientation, by distance A. In one example,distance A may be 50 μm. Transition stripe L1, having a second azimuthalorientation, is separated from transition stripe L3, also having asecond azimuthal orientation, by distance B. In one example, distance Bmay be 100 μm (“B” distance).

As illustrated in FIG. 2, in the prior art, each burst of transitionstripes within one servo band (e.g. 27 a) is longitudinally aligned witheach burst of transition stripes of all servo bands (e.g. 27 b, 27 c, 27d, 27 e). For example, the burst represented by transition stripe L1 ofservo band 27 a aligns longitudinally with the burst represented bytransition stripe M1 of servo band 27 b along x1. Similarly, the burstsrepresented by transition stripes L2 and L3 align longitudinally withthe bursts represented by transition stripes M2 and M3, respectively.

Servo read element 25 (as shown in FIG. 1) measures the “A” distancealong servo band 27 a by detecting a signal as it crosses a transitionstripe of a first azimuthal orientation of servo band 27 a (e.g.transition stripe L2) along servo track centerline 50 and then bydetecting a signal as it crosses an adjacent transition stripe of asecond azimuthal orientation of servo band 27 a (e.g. transition stripeL3). Similarly, servo read element 26 measures the “A” distance alongservo band 27 b by detecting a signal as it crosses a transition stripeof a first azimuthal orientation of servo band 27 b (e.g. transitionstripe M2) along servo track centerline 50 and then by detecting asignal as it crosses an adjacent transition stripe of a second azimuthalorientation of servo band 27 b (e.g. transition stripe M3). Since thetransition stripes L3 and M3 align longitudinally along the length ofthe magnetic tape 20 at x2, the servo read element 25 outputs servoinformation regarding distance “A” at the same time that servo readelement 26 outputs information regarding distance “A”. Accordingly,servo information obtained from servo element 26 regarding an odd servoband is provided simultaneously with the servo information obtained fromservo element 25 regarding an even servo band.

Furthermore, as illustrated in FIG. 2, servo read element 25 measuresthe “B” distance along servo band 27 a by detecting a signal as itcrosses a transition stripe of a second azimuthal orientation of servoband 27 a (e.g. transition stripe L1) along servo track centerline 50and then by detecting a signal as it crosses an adjacent transitionstripe of the second azimuthal orientation of servo band 27 a (e.g.transition stripe L3). Similarly, servo read element 26 measures the “B”distance along servo band 27 b by detecting a signal as it crosses atransition stripe of a second azimuthal orientation of servo band 27 b(e.g. transition stripe M1) along servo track centerline 50 and then bydetecting a signal as it crosses an adjacent transition stripe of thefirst azimuthal orientation of servo band 27 b (e.g. transition stripeM3). Again, since the transition stripes L3 and M3 align longitudinallyalong the length of the magnetic tape 20 at x2, the servo read element25 outputs servo information regarding distance “B” at the same timethat servo read element 26 outputs information regarding distance “B”.Accordingly, servo information obtained from servo element 26 regardingan odd servo band is provided simultaneously with the servo informationobtained from servo element 25 regarding an even servo band.

The sample rate, Fs, of the servo read element signal is determined bythe length of the servo pattern and the tape velocity. The samplingrate, Fs may be expressed as: ${Fs} = \frac{velocity}{distance}$wherein the velocity is the velocity of the magnetic tape and thedistance is the distance between two transition lines of the servopattern.

For example, assuming a tape velocity of 2 m/sec, a distance “A” of 50μm, and a distance “B” of 100 μm, the servo read elements 25 and 26would output servo information at a rate of 20,000 samples every second.

The sample rate required for proper serving is determined by the rest ofthe components of the track-following servo loop. In order to support ahigh bandwidth track following the servo control system requires a highsampling rate servo feedback signal. The high sampling rate providesup-to-date, accurate information of the servo read element position, andtherefore, supports a higher servo bandwidth and thus a much bettercontrolled servo system. As the magnetic tape 20 velocity slows to matchwith the slower data transfer host system (referred to as speedmatching) the sampling rate becomes slower and results in too slow of asampling rate to maintain high bandwidth track following system.

Thus, what is presented is tape cartridge having a servo pattern with ahigher longitudinal density of servo information such that a higherservo sampling rate is realized. The higher sampling rate providesup-to-date accurate information of servo read element position and,therefore, ensures a higher servo bandwidth system with increasedcontrol.

In accordance with the present disclosure FIG. 3 describes a timingbased servo pattern on a magnetic tape, such as magnetic tape 320wherein prerecorded magnetic parallel longitudinal servo tracks 327 a,327 b, 327 c, 327 d, and 327 e (also referred to herein as 327) liebetween groups of longitudinal data tracks 329 a, 329 b, 329 c, 329 d,and 329 e (herein after referred to as 329). In addition, theprerecorded magnetic parallel servo tracks or bands comprise odd servobands and even servo bands. The odd servo bands lie between each of theeven servo bands. For example, servo bands 327 a, 327 c and 327 e may bedefined as even servo bands and servo bands 327 b, and 327 d may bedefined as odd servo bands.

The magnetic tape 320 is also provided with guard bands 348, 349 at theedges of the tape. The longitudinal direction is defined as thedirection along the length of the magnetic tape 320. The lateraldirection is defined as the direction along the width of the magnetictape 320 and is perpendicular to the longitudinal direction.

In the example of FIG. 3, five longitudinal timing based defined servobands 327 are prerecorded on a magnetic tape 320 for track following atthese positions. The pattern of magnetic transitions recorded in thedefined servo bands is a repeated set of frames 338, each of which areof different azimuthal orientations. For example, the pattern maycomprise transitions slanted, or having an azimuthal orientation, in afirst direction with respect to the longitudinal direction of the linearservo track, alternating with transitions having different slants, forexample, in the opposite direction. The groups of transitions having thesame azimuthal orientation and separated by gaps or spaced are referredto as “servo bursts” or simply as “bursts” (e.g. bursts 340, 341, 342,and 343). Each servo burst contains a predetermined number of transitionstripes per burst, which can be used in error detection and correction.As shown in FIG. 3, the present embodiment comprises a first burst of agroup of five stripes in a first azimuthal orientation and a secondburst of a group of five transitions in a second azimuthal orientationdifferent than the first azimuthal orientation, followed by a thirdburst of a group of four transition stripes in the first azimuthalorientation and a fourth burst a group of four transition stripes in thesecond azimuthal orientation.

The head assembly 324 comprises a plurality of read and/or writeelements 328 configured to read and/or write data on a magnetic tapewith respect to sets of the longitudinal data tracks 329. When the servoread elements 325, 326 are properly positioned at the defined servobands 327, the read and write elements 328 are properly positioned totransfer data with respect to the data track location of the magnetictape 320.

The lateral positioning of the servo read element with respect to thetiming based servo track is sensed based on a measure of time betweentwo transitions having different slants, called the “A” distance, ascompared to the time between two transitions having parallel slants,called the “B” distance. Referring to FIG. 3 for example, the “A”distance may be measured based on the time between the first transitionstripe of burst 340 and the first transition stripe of burst 341.Further, in one example, the “B” distance is measured based on the timebetween the first transition stripe of burst 340 and the firsttransition stripe of burst 342. One of ordinary skill in the art wouldunderstand that while in the above example the first transition stripeof each burst is used to determine the “A” and “B” distance, anytransition stripe of the respective burst may be utilized. For example,the “A” and “B” distances may be determined based on the comparison ofthe second transition stripe of one burst against the second transitionstripe of the other burst.

More generally, lateral position sensing within a defined servo band isachieved by deriving a ratio of these two servo pattern intervals.Specifically, the lateral position may be the ratio of (1) the distancebetween transitions of bursts 340 and 341, called the “A” distance, to(2) the distance between transitions of burst 340 and 342, called the“B” distance. The distances are measured by the timing between thetransitions at a constant velocity. Thus, as the tape head servo readelements 325, 326 move toward the lower edge of the magnetic tape 320,the ratio of the time between the transitions of burst 340 and 341 tothe time between the transitions of bursts 340 and 342 becomes greater,since the distance between the “A” transitions of the burst 340 and 341is greater, while the distance between the “B” transitions of burst 340and 342 remains unchanged.

As illustrated in FIG. 3, each burst of transition stripes within theodd servo bands (e.g. 327 b and 327 d) is longitudinally shifted or isoffset from each burst of transition stripes of the even servo bands(e.g. 327 a, 327 c, and 327 e) such that the servo information of saidodd servo bands is interleaved with the servo information from the evenservo bands.

FIG. 4 shows simplified version of a timing based servo pattern on amagnetic tape, such as magnetic tape 320. For purposes of simplifyingthe illustration each burst is shown in FIG. 4 as a single line. In oneembodiment the single line may represent the first transition stripe ofeach burst.

Similar to that described with respect to FIG. 3, the head assembly 324comprises at least two narrow servo read elements 325, 326, allowing twoservo bands (e.g. 327 a and 327 b) to be sensed simultaneously. Asmentioned above, when a servo read element (e.g. servo read element 325and/or 326) crosses a transition of servo track 327, e.g. along servotrack centerline 350, it produces an analog signal pulse whose polarityis determined by the polarity of the transition.

In the example illustrated in FIG. 4 transition stripe L2, having afirst azimuthal orientation, is separated from transition stripe L3,having a second azimuthal orientation, by distance “A”. In one example,distance “A” may be 50 μm. Transition stripe L1, having a secondazimuthal orientation, is separated from transition stripe L3, alsohaving a second azimuthal orientation, by distance “B”. In one example,distance “B” may be 100 μm.

As illustrated in FIG. 4, each burst of transition stripes within theodd servo bands (e.g. 327 b and 327 d) is longitudinally shifted or isoffset from each burst of transition stripes of the even servo bands(e.g. 327 a, 327 c, and 327 e). For example, the burst represented bytransition stripe M1 of servo band 327 b is longitudinally shifted fromthe burst represented by transition stripe L1 of servo band 327 a by adistance “D”. Similarly, the bursts represented by transition stripe L2and L3 are longitudinally shifted from the bursts represented bytransition stripe M2 and M3 by a distance “D”, respectively. It shouldbe understood by one of ordinary skill in the art, that while notlabeled, 327 c and 327 e contain L1, L2, and L3. As shown in FIG. 4transitions L1, L2, and L3 of 327 c and 327 e align with L1, L2, and L3of 327 a, respectively. Similarly, 327 d contains M1, M2, and M3. Asshown in FIG. 4 transitions M1, M2, and M3 of 327 d align with M1, M2and M3 of 327 b, respectively.

Servo read element 325 measures the “A” distance along servo band 327 aby detecting a signal as it crosses a transition stripe of a firstazimuthal orientation of servo band 327 a (e.g. transition stripe L2)along servo track centerline 350 and then by detecting a signal as itcrosses an adjacent transition stripe of a second azimuthal orientationof servo band 327 a (e.g. transition stripe L3). Similarly, servo readelement 326 measures the “A” distance along servo band 327 b bydetecting a signal as it crosses a transition stripe of a firstazimuthal orientation of servo band 327 b (e.g. transition stripe M2)along servo track centerline 350 and then by detecting a signal as itcrosses an adjacent transition stripe of a second azimuthal orientationof servo band 327 b (e.g. transition stripe M3). Since the transitionstripes L3 and M3 are longitudinally shifted from each other by adistance “D”, the servo read element 325 outputs servo informationregarding distance “A” at a different time than when servo read element326 outputs information regarding distance “A” such that the servoinformation of the odd servo bands is interleaved with the servoinformation from the even servo bands. Accordingly, servo informationobtained from servo element 326 regarding an odd servo band is notprovided simultaneously with the servo information obtained from servoelement 325 regarding an even servo band.

Furthermore, as illustrated in FIG. 4, servo read element 325 measuresthe “B” distance along servo band 327 a by detecting a signal as itcrosses a transition stripe of a second azimuthal orientation of servoband 327 a (e.g. transition stripe L1) along servo track centerline 350and then by detecting a signal as it crosses an adjacent transitionstripe of the second azimuthal orientation of servo band 327 a (e.g.transition stripe L3). Similarly, servo read element 326 measures the“B” distance along servo band 327 b by detecting a signal as it crossesa transition stripe of a second azimuthal orientation of servo band 327b (e.g. transition stripe M1) along servo track centerline 350 and thenby detecting a signal as it crosses an adjacent transition stripe of thesecond azimuthal orientation of servo band 327 b (e.g. transition stripeM3). Again, since the transition stripes L3 and M3 are longitudinallyshifted by a distance “D” the servo read element 325 outputs servoinformation regarding distance “B” at a time different than when theservo read element 326 outputs information regarding distance “B”.Accordingly, servo information obtained from servo element 326 regardingan odd servo band is not provided simultaneously with the servoinformation obtained from servo element 325 regarding an even servoband.

Distance “D” may be expressed by the following equation, wherein X isthe number of laterally spaced servo read elements of magnetic tapedrive: $\begin{matrix}{{\lbrack {\frac{1}{X} - {{.1}( \frac{1}{X} )}} \rbrack B} \leq D \leq {\lbrack {\frac{1}{X} + {{.1}( \frac{1}{X} )}} \rbrack B}} & ( {{Equation}\quad 1} )\end{matrix}$wherein X is the number of laterally spaced servo read elements of amagnetic tape drive configured to read and/or write to magnetic tape320. Equation 1 may be simplified as follows: $\begin{matrix}{{0.9\frac{B}{X}} \leq D \leq {1.1{\frac{B}{X}.}}} & ( {{Equation}\quad 2} )\end{matrix}$

In one embodiment, tape 320 is to be utilized in a magnetic tape drivehaving two laterally spaced apart servo read elements 325, 326. In thisembodiment the first transition stripe of each burst of each odd servoband is longitudinally shifted from the first transition stripe of eachburst of each even servo band by a substantially equal distance “D”,wherein D is between 0.45B and 0.55B. In a further embodiment thedistance “D” is approximately 0.50B. Therefore, in the embodiment inwhich two servo read elements read two different servo bands (e.g. 327 aand 327 b) the head assembly 324 will output servo information for theeven servo band 327 a at a different time than that of any adjacentservo band (e.g. odd servo band 327 b). Similarly, servo read element325 will output servo information for the odd servo band 327 b at adifferent time than that of any adjacent servo bands (e.g. 327 a and 327c). Therefore, each burst of transition stripes within the odd servobands (e.g. 327 b and 327 d) is longitudinally shifted or is offset fromeach burst of transition stripes of the even servo bands (e.g. 327 a,327 c, and 327 e) such that the servo information of said odd servobands is interleaved with the servo information from the even servobands. The above described pattern provides a sampling rate that isdoubled over the prior art pattern.

For example in the present embodiment, assuming a tape velocity of 2m/sec and wherein distance “A” is 50 μm, and distance “B” is 100 μm, theservo read elements 325 and 326, would output servo information at arate of 40,000 samples every second because the odd servo band patternis shifted longitudinally shifted from the even servo pattern by adistance of “D”, wherein 0.45B≦D≦0.55B.

Returning to FIG. 3, the tape is moved longitudinally across the headassembly 324 so that the servo tracks 327 a and 327 b are moved acrossthe servo read elements 325 and 326, respectively. When such movementoccurs, the servo pattern of magnetic flux transitions is detected bythe servo read elements 325 and 326 so that it generates two analogservo read element signals, one for each servo read elements 325 and326. As described above, in the present embodiment the first transitionstripe of each burst of each odd servo band (e.g. 327 b) islongitudinally shifted from the first transition stripe of each burst ofsaid even servo band (327 a) by a substantially equal distance, “D”,such that servo information of the odd servo band (327 b) is interleavedwith said servo information from the even servo band (327 a). The analogservo read element signals for each servo read elements 325 and 326 areprovided via a servo signal lines 384 and 390 to signal decoders 386 and392, respectively. Because of the longitudinal shift the servo signalsfor the even servo band (327 a) and odd servo band (327 b) are generatedat different times and the respective signal decoders process the servoread element signals separately and generate a position signal that istransmitted via position signal lines 388 and 394 to servo controller380. The servo controller 380 generates a servo control signal for eachservo band (e.g. 327 a and 327 b) and provides it on control line(s) 382to a servo positioning mechanism at head assembly 324. The servopositioning mechanism responds to the control signal from the servocontroller 380 by moving the assembly including servo read elements 325and 326 laterally with respect to the servo track centerline 350 foreach servo band respectively (e.g. 327 a and 327 b) to reach the desiredservo track or to maintain the servo read elements 325 and 326 centerwith respect to the servo track centerline 350.

Servo detection logic of servo controller 380 is configured to detectfrom the signals supplied on line(s) 382, the relative timings of thelaterally extending transitions, specifically including the transitionshaving different slants, sensed by the plurality of laterally spacedservo read elements 325 and 326 as the magnetic tape 320 is moved in thelongitudinal direction. The servo detection logic is configured todetermine from the relative timings of the sensed transitions the “A”distances and information regarding the relationship between theplurality of servo read elements 325 and 326 and the magnetic tape forat least one known set of laterally extending transitions havingdiffering slants.

A magnetic tape drive 100 is illustrated in FIG. 5 configured to readand/or write data to a magnetic tape 320, for example, from a magnetictape cartridge 103. The magnetic tape drive 100 is configured to receivethe magnetic tape cartridge 103, and the magnetic tape 320 is guidedalong a tape path from the magnetic tape cartridge, past a head assembly324, to a take up reel 105. The magnetic tape 320 may be guided by tapeguide rollers 110 along the tape path and constrained laterally by thetape guide rollers as the magnetic tape is moved longitudinally betweenthe magnetic tape cartridge 103 and the take up reel 105, for example,by a drive system comprising drive motors and a servo drive control (notshown).

Although the magnetic tape 320 is constrained laterally by the tapeguide rollers 110, some minor lateral movement may still occur at thehead assembly 324. Further, the magnetic tracks may have some minorlateral movement on the magnetic tape. A servo system 380 is configuredto move the head assembly 324, comprising the servo read elements 325and 326 and read and/or write heads 328 of FIGS. 3 and 4, laterally withrespect to the magnetic tape 320 in accordance with the informationrelating to the lateral position, discussed above, for example, to trackfollow the servo tracks of the magnetic tape 320.

Magnetic tape cartridge 103 is illustrated in further detail in FIG. 6.The magnetic tape cartridge 103 may include a cartridge memory (CM) 614(shown in cutaway) and magnetic tape 320 (shown in phantom) wound on ahub 612 of a reel 613. If present, the cartridge memory 614 may compriseelectrical contacts to allow a library (not shown) and/or magnetic tapedrive 100 (as seen in FIG. 5) to access the contents of the cartridgememory 614. Alternatively, the cartridge memory 614 may comprise acontactless interface such as induction, radio frequency, or optical. Inone embodiment, the cartridge memory 614 comprises an RFID tag. Thecartridge memory 614 may be used to hold information about the tapecartridge 103, the magnetic tape 320 in the tape cartridge 103, and/ordata on the magnetic tape 320. Examples of tape cartridges are acartridge based on LTO (Linear Tape Open) technology, such as the IBMTotalStorage LTO Ultrium Data Cartridge, and a cartridge based on IBM's3592 technology, such as the IBM 3592 Enterprise Tape Cartridge. As willbe appreciated, the tape cartridge 103 may be a magnetic tape cartridgehaving a dual reel implementation (in which the tape is fed betweenreels within the cartridge) or single reel implementation, such asillustrated in FIG. 6, in which the magnetic tape 320 is wound on a reel613 within the magnetic tape cartridge 103. For example, when themagnetic tape cartridge 103 is loaded into a magnetic tape drive (e.g.magnetic tape drive 100), the tape is fed between the cartridge reel 613and a take up reel 105 located in the magnetic tape drive 100. Whileexemplary tape cartridges based on the LTO and 3592 formats have beenprovided, it will be appreciated that the description is not limited bytape format. Examples of other tape formats include DLT, SDLT, 9840,9940, T10000, AIT, and the like.

As discuss above, the magnetic tape 320 of tape cartridge 103, has servoinformation in prerecorded magnetic longitudinal servo tracks for trackfollowing at these positions. Each burst of transition stripes withinthe odd servo bands (e.g. 327 b and 327 d) is longitudinally shifted oris offset from each burst of transition stripes of the even servo bands(e.g. 327 a, 327 c, and 327 e) by a substantially equal distance “D” asdefined by Equation 2 above.

Since the transition stripes are longitudinally shifted from each otherby a distance “D”, the servo read element 325 outputs servo informationregarding distance “A” at a different time than when servo read element326 outputs information regarding distance “A”. Similarly, the servoread element 325 outputs servo information regarding distance “B” at adifferent time than when servo read element 326 outputs informationregarding distance “B”. Accordingly, servo information obtained fromservo element 326 regarding an odd servo band is not providedsimultaneously with the servo information obtained from servo element325 regarding an even servo band. Therefore, the servo information ofthe odd servo bands is interleaved with the servo information from theeven servo bands.

In one embodiment the distance “D” is between 0.45B and 0.55B. In afurther embodiment the distance “D” is 0.50B. The above describedpattern on a magnetic tape 320 of tape cartridge 103 provides a samplingrate that is doubled over the prior art patterns.

For example, in the present embodiment, assuming a tape velocity of 2m/sec, a distance “A” of 50 μm, and a distance “B” of 100 μm, the servoread elements 325 and 326, would output servo information at a rate of40,000 samples every second since the odd servo band pattern is shiftedlongitudinally shifted from the even servo pattern by a distance of “D”,wherein 0.45B≦D≦0.6B.

While the above described embodiment discusses a head assemblycomprising two servo read elements, a head assembly may comprise anynumber of servo elements. For example, in another embodiment, the headassembly 324 comprises three servo read elements. Accordingly, eachburst of transition stripes within one servo band is shifted or isoffset a substantially equal distance “D” from the burst of transitionstripes of the previous servo band. In one embodiment, in which threeservo read elements are utilized the distance “D” is between 0.30B and0.37B as described by Equation 2. In a further embodiment, the distance“D” is approximately 0.33B.

For example, each burst of transition stripes of servo band 327 b willbe shifted longitudinally a distance “D” of approximately 0.33B fromeach burst of transition stripes of servo band 327 a. Similarly, eachburst of transition stripes of servo band 327 c will be shiftedlongitudinally a distance “D” of approximately 0.33B from each burst oftransition stripes of servo band 327 b. Further, each burst oftransition stripes of servo band 327 d will be shifted longitudinally adistance “D” of approximately 0.33B from each burst of transitionstripes of servo band 327 c such that the transition stripes of servoband 327 d is aligned with the transition stripes of servo band 327 a.Finally, each burst of transition stripes of servo band 327 e will beshifted longitudinally a distance “D” approximately 0.33B from eachburst of transition stripes of servo band 327 d such that the transitionstripes of servo band 327 e is aligned with the transition stripes ofservo band 327 b.

Similar to that discussed above with respect to FIGS. 3 and 4, since thetransition stripes are longitudinally shifted from each other by adistance “D”, each of the servo read elements output servo informationregarding distances “A” and “B” at a different time than any adjacentservo band. For example, in the embodiment in which three servo readelements read three different servo bands (e.g. 327 a, 327 b, and 327 c)the head assembly 324 (with three servo heads, not shown) will outputservo information for servo band 327 b at a different time than that anyadjacent servo band (e.g. 327 a and 327 c) such that the servoinformation of said odd servo bands is interleaved with the servoinformation from the even servo bands, and specifically, that the servoinformation of a servo band is interleaved with the servo informationfrom any adjacent servo band. The above described pattern provides asampling rate that is tripled over the prior art pattern.

For example, in the present embodiment, assuming a tape velocity of 2m/sec, a distance “A” of 50 μm, and a distance “B” of 100 μm, the servoread elements 325 and 326, would output servo information at a rate of60,000 samples every second since each burst of transition stripeswithin one servo band is shifted or is offset a substantially equaldistance “D” from the burst of transition stripes of the previous servoband, wherein 0.30 B≦D≦0.37B.

It should be understood by one of ordinary skill in the art that whilethe above description describes magnetic transition stripes recorded onmagnetic tape, it should be understood that the servo bands 327 maycomprise any of several types of longitudinal servo patterns as is knownto those of skill in the art.

While the present embodiment describes servo bands 327 a, 327 c, and 327e as even servo bands and 327 b, and 327 d as odd servo bands, it shouldbe understood by one of ordinary skill in the art that 327 a, 327 c, and327 e may be defined as odd servo bands and 327 b, and 327 d may bedefined as even servo bands. Rather, it is only important that eachburst of transition stripes within one servo band (is longitudinallyshifted or is offset from each burst of transition stripes of anyadjacent servo band by a substantially equal distance, “D”.

Further, while the present disclosure describes a magnetic tape 320having five servo bands and four data bands, the present disclosure maybe practiced on any magnetic tape having a plurality of servo bands.

The logic discussed above may comprise any suitable logic arrangementknown to those of skill in the art. Further, those of skill in the artwill understand that differing specific component arrangements may beemployed than those illustrated herein.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims.

1. A magnetic tape cartridge, comprising: a magnetic tape, said magnetictape having servo information comprising: a plurality of parallellongitudinal servo bands that lie between a plurality of longitudinaldata bands; said plurality of servo bands comprise odd servo bands andeven servo bands, wherein each of said odd servo bands lie between saideach of said even servo bands; each of said plurality servo bandscomprising a plurality of frames, wherein each frame comprises aplurality of bursts of transition stripes, each burst having a firsttransition stripe; said first transition stripe of each burst of eachsaid odd servo band is longitudinally shifted from said first transitionstripe of each burst of each said even servo band by a substantiallyequal distance, D, such that said servo information of said odd servobands is interleaved with said servo information from said even servobands.
 2. The magnetic tape cartridge of claim 1, wherein said framefurther comprises a first burst of transition stripes in a firstazimuthal orientation and a second burst of transition stripes in asecond azimuthal orientation different than said first azimuthalorientation, followed by a third burst of transition stripes in saidfirst azimuthal orientation and a fourth burst of transition stripes insaid second azimuthal orientation and wherein a distance between saidfirst transition stripe of said first burst and said first transitionstripe of said third burst is a distance B.
 3. The magnetic tape ofclaim 2, wherein said magnetic tape is configured for a tape drivehaving a plurality of servo read elements, said first transition stripeof each burst of each said odd servo band is longitudinally shifted fromsaid first transition stripe of each burst of each said even servo bandby said substantially equal distance, D, wherein${0.9\frac{B}{X}} \leq D \leq {1.1\frac{B}{X}}$ and wherein X is anumber servo read elements of said tape drive.
 4. The magnetic tape ofclaim 3, wherein said magnetic tape is configured for a tape drivehaving two servo read elements such that 0.45B≦D≦0.55B.
 5. The magnetictape of claim 3, wherein said magnetic tape is configured for a tapedrive having three servo read elements such that 0.30B≦D≦0.37B.
 6. Themagnetic tape of claim 2, wherein 0.45B≦D≦0.55B.
 7. The magnetic tape ofclaim 6, wherein D is approximately 0.50B.
 8. The magnetic tape of claim2, wherein 0.30B≦D≦0.37B.
 9. The magnetic tape of claim 6, wherein D isapproximately 0.33B.
 10. The magnetic tape cartridge of claim 1, whereinsaid second azimuthal orientation is opposite of said first azimuthalorientation.
 11. The magnetic tape cartridge of claim 1, wherein saidmagnetic tape comprises five parallel longitudinal servo bands.
 12. Themagnetic tape cartridge of claim 1, wherein said frame further comprisesa first burst of a group of five stripes in a first azimuthalorientation and a second burst of a group of five transitions in asecond azimuthal orientation different than said first azimuthalorientation, followed by a third burst of a group of four transitionstripes in said first azimuthal orientation and a fourth burst a groupof four transition stripes in said second azimuthal orientation.
 13. Atape cartridge, comprising: a tape, said tape having servo informationcomprising: a plurality of parallel longitudinal servo bands that arepositioned between a plurality of longitudinal data bands; saidplurality of servo bands comprise odd servo bands and even servo bands;each of said plurality servo bands comprising a plurality of frames,wherein each frame comprises a plurality of bursts of transitionstripes, each burst having a first transition stripe; said firsttransition stripe of each burst of each said odd servo band islongitudinally shifted from said first transition stripe of each burstof each said even servo band by a substantially equal distance, D, suchthat said servo information of said odd servo bands is interleaved withsaid servo information from said even servo bands.